There is known a vehicle driving system which include an internal combustion engine, an electric motor and a compressor for an air conditioner which controls the humidity, ventilation, and temperature in a passenger compartment of a vehicle (for example, refer to Patent Literature 1).
As shown in FIG. 16, a vehicle driving system 200 of Patent Literature 1 has a twin-clutch type transmission mechanism which includes a first input shaft 202a that is connected to an electric motor 210 and which is selectively coupled with an internal combustion engine output shaft 204 by a first engaging and disengaging unit 205, a second input shaft 202b which is selectively coupled with the internal combustion engine output shaft 204 by a second engaging and disengaging unit 206, an output shaft 203 which outputs a driving force to a driven portion, a first gearset including plural gears that are disposed on the first input shaft 202a and which are selectively coupled with the first input shaft 202a via first synchronizers 230, 231, a second gearset including plural gears that are disposed on the second input shaft 202b and which are selectively coupled with the second input shaft 202b via second synchronizers 216, 217, and a third gearset including plural gears that are disposed on the output shaft 203 and which mesh with the gears of the first gearset and the gears of the second gearset. An air conditioning compressor 260, which is an auxiliary device, is coupled with the electric motor 210 via an air conditioning clutch 261.